I wonder whether a whitewater kayaking life jacket might be the ticket for some of you guys. Some of them have a built in harness but it is setup to work off the back(they primarily are used for towing). If you clipped in off the front side of the jacket, I would think that would be what you are looking for. Whitewater jackets are not like normal lifejacket, they are built much stronger and are often type V.

If this interests you, check out Astral Buoyancy, Kokatat, and there are a few others. Just make sure that the tow harness can be accessed in the front.